Broadcasting system



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l R. D. DUNCAN, JR

' BROADCASTING sYsTxn Filed' Jung V11. 1928.

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'-ATWTORNEY April 2, 1935. R. D. DUNCAN, JR 1,996,149

BROADCASTING SYSTEM Filed June 11, 192s :s sheets-sheet 2 Q 'n /LJ ,Em S.'\

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R. D. DUNCAN, JR

BROADCASTING SYSTEM Filed June' 11, 1928 's sheets-sheet s INVENTm F0 er m'azz, Jr. l

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Patented Apr. 2, 1935 UNITED STATES PATENT OFFICE BROADCASTING SYSTEM Ware Application June 11, 1928, Serial No. 284,577

4 Claims.

My invention relates to broadcasting systems in general and more specifically to wired radio systems of the type wherein high frequency currents are modulated and transmitted over wire lines which may be simultaneously employed for the transmission of electric power.

An object of my invention is to provide a means for blocking the flow of high frequency current, from a wire circuit which is simultaneously supplying electric power, without substantially aliecting the passage of power over the circuit or the passage of high frequency current over adjacent wire circuits.

Another object of my invention is to provide a means for preventing the reception of wired radio signals from a wire circuit which is simultaneously supplying electric power.

Still another object of my invention is to provide a wired radio system whereby interference, 20 from disturbing currents arising at any point on the system, is prevented from extending to an appreciable wire distance over the system.

A further object of my invention is to provide a system for the reception of radio signals without interference from disturbing currents in adjacent transmission lines.

A better understanding can be had of the system I employ by reference to the specification to follow and to the accompanying drawings in which:

Figure 1 is a diagrammatic illustration of one embodiment of my invention; Fig. 2 is a diagrammatic illustration of an embodiment of my invention showing how my invention may be employed to prevent the passage of signaling current over a certain circuit and to prevent interference from disturbing currents; Fig. 3 shows how my invention may be employed with a three wire power circuit; Fig. 4 is a diagramma- 40 tic illustration showing a number of applications of my invention and the manner in which it is employed; and Fig. 5 illustrates a method of connecting my invention to a power system and shows how the signal blocker may be mounted.

In the system of wired radio broadcasting wherein high frequency currents, modulated in accordance with voice or music frequencies, are superimposed upon the electric light and power lines of a city or community it at times becomes necessary to block the passage of these currents from circuits which supply certain electric power consumers and thus prevent the reception of signals from the 110 volt (or 110-220 volt) lines, to which the wired radio receiver located in the consumers home is normally connected, Such a condition may arise when an electric lighting customer refuses to rent or purchase an authorized receiver and attempts to receive the wired radio broadcasting with an unauthorized receiver.

Again it hasl been determined that certain types 6 of household electric appliances, such as the vibrator type of storage battery charger, electric oil burner, etc. may cause considerable interference with wired radio reception. This type of interference is easily eliminated by the installation of means described in co-pending application Serial No. 293,099 iled July 16, 1928, immediately at the device in question. Occasions have arisen when the electric lighting customer has refused to allow the installation of interference preventing means and has continued to operate the device thus causing considerable interference with the wired radio broadcast reception by other consumers.

In both cases it is necessary to electrically isolate the consumer or consumers in question in such a manner that the reception of wired radio broadcasting is prevented, and that whatever electrical disturbance may originate at that point is prevented from affecting other consumers. It must be remembered however, that the electric light and power service must not be interrupted.

Some of the advantages of my system are that it effectively blocks the passage of carrier frequency currents over a wide range of frequencies corresponding to the frequency band required by the total number of programs broadcast. It allows the cycle, 110 volt power current to be supplied to the consumer without appreciable voltage drop. My invention is simple and rugged and may be installed where it is inaccessible to the consumer and affects only the consumer in question.

An embodiment of my invention is shown diagrammatically in Fig. 1, wherein I represents one 0 form of my invention in its entirety, consisting of an inductance 2, in series with line 4 and a capacity 3 connected between lines 4 and 5. Signal blocker I as normally employed is connected in the 11,0 volt secondary service to the con- 45 sumer, prior to the consumers service switch, that is, between the transformer secondary and the watt-hour meter. This is illustrated in Fig. 1 and in Fig. 2 wherein lines 4 5 are indicated as extending to the right to connect with the sec- 50 ondary of the transformer. In Fig. 2 as before,

l represents the signal blocker installed in the volt lines prior to their entrance to the consumers home indicated at 6. Lines 4-5 connect with the service switch 1, watt-hour meter 5 8, and to circuits I0 and II of consumers home. The consumers loads are represented as lights I2, fan I3, unauthorized wired radio receiver I4, battery charger I5 and a charging storage battery I6.

A common form of electric power system employs three wires with 110 volts between each of the outside wires and center wire which is neutral. A signal blocker suitable for such a service is illustrated in Fig. 3 wherein I1 represents the device in its entirety including in combination two units of the type shown at I of Fig. 1, comprising inductances I8 and I9 in series with the two outside wires 56 of the HIJ-220 volt service and condensers 20 and 2l connected between each of the outside wires 58 and the neutral wire 51.

The signal blocker described in co-pending application Serial No. 592,952, led October 10, 1922, utilizes a parallel tuned circuit in series with the customers service. Though highly effective at a single frequency and over a narrow band in the immediate vicinity of this frequency, such a blocker is not suilicientl'y effective over a wide range of frequencies. Viewed from the service switch the 110 volt house wiring at carrier frequencies has the properties of a resistance of value in the neighborhood of l0 to 30 ohms. Connecting a condenser having an approximate capacity of one microfarad across the lines at the service switch is in effect, at carrier frequencies, connecting a low impedance in parallel with another low impedance. The bypassing effect of the condenser would not be appreciable and the practical result is that only small and insufficient reduction of signal strength is obtained. The use of a relatively high inductance in series with the service leads is also partially effective, becoming more pronounced with increasing frequency. The use of a series inductance is restricted however by virtue of the fact that it must pass the 60 cycle power current without producing an appreciable voltage drop. This loss limits the size of the inductance which may be economically employed. The combined use of a condenser connected across the lines and an inductance in series when both are of the proper value, has been found to be entirely effective in suppressing the wired radio signal, that is, in blocking the flow of carrier frequency currents from the power transformer secondary or from the power lines to the 110 volt house wiring of the consumer. An inductance having a value of 0.0005 henry in combination with a capacity of 2 microfarads has been found to operate satisfactorily to give substantially a complete elimination of signal over the range of approximately 25 to '10 kilocycles such as is normally employed in wired radio broadcasting. The preferred form of connection is that illustrated in Figs. l, 2, 3 and 4, wherein the condenser is connected across the lines on the customers side of the series inductance. This method of connection insures that the condenser will not affect the signals re'- ceived from the lines by other consumers supplied from the same transformer. This is an important feature. This method of connection prevents interference arising within the consumers premises, such as from the operation of storage battery charger as at I5 of Fig. 2, from reaching the power lines and affecting other consumers.

One method for installation of the noise or signal blocker is illustrated in Fig. 5 wherein 22 represents a three phase, three conductor primary line, 23 a transformer with its primary connected to one phase and secondary connected with secondary leads 24 which supply the consumers house 26. The signal blocker is shown installed at 25, prior to the entrance of the secondary lines into the consumers premises.

Another method of installation and use of signal blockers is further illustrated in Fig. 4, wherein the numeral 21 in its entirety represents an electric substation or power house, and 28, 29 and 38 consumers premises. 3l represents the normal electric power generating and transformer equipment contained in the substation or power house and is shown supplying primary lines 32 and 33. These are represented as three phase, three conductor lines. Lines 32 show transformers 34, 35 and 36 connected respectively between each of the three phases. Lines 33 are assumed to have similar transforming connections throughout their length. In the substation 21 the high frequency wired radio transmitter is indicated at 31, having a modulating means 38 connected thereto which is supplied by microphone 39. The latter may be in the substation or connected with 38 through telephone lines extending from the substation. Wired radio sender 31 is shown connected to each of the three lines 32 through coupling condensers 40. As illustrated herewith, wired radio sender 31 would be of the three phase type. Only a single channel sender is represented but this in no way affects the operation of the system.

Transformer 34 is shown having its secondary supplying directly the consumer 28 through service switch 4I and watt-hour meter 42. The consumers lamp load is represented at 43 and an authorized wired radio receiver at 44. Transformer 35 is shown having its secondary supplying consumers 29 and 30, through signal blockers 45 and 46 respectively. The service to the consumer 29 is shown to be 110-220 volt, three-wire and that to consumer 30, 110 volt, two wire. The secondary lines extend through the signal blockers 45 and 46 respectively to service switches 41 and 48, watt-hour meters 49 and 50, to the consumers loads indicated at 5I and 52. An unauthorized wired radio receiver is shown at 53. A battery charger, which may be of the vibrator type is shown at 54 charging storage battery 55.

With the system as illustrated in Fig. 4, consumer 28 will receive on authorized wired radio receiver 44 the wired radio broadcast material transmitted from sender 31, 38, 39, whereas consumer 29 will be unable to receive this service because of the inclusion of signal blocker 45 in the secondary leads of transformer 35 supplying his electric power service. His normal 60 cycle electric power is not interfered with, however. The battery charger 54 shown at consumer 30 will not cause interference with wired radio broadcast reception at consumer 28 because of the presence of signal blocker 46, which in this instance functions both as a signal blocker for signals received from transformer 35 and as a noise blocker or interference preventer for electrical distubances arising in the house wiring of consumer 3U.

The foregoing description relates to the use of signal blockers on an alternating current electric power distribution system. It is obvious that they will work equally well on direct current distribution systems, and the scope of this invention is not to be restricted to this specification or to the accompanying drawings. Nor should the scope of this invention be restricted to only one substation and three consumers as shown in Fig. 4. It is obvious that a wired radio broadcasting system will consist of a number of substations and a great number of electric power consumers.

Reference is also made in the foregoing specication to the use of an inductance of Y0.0005 henry and a capacity of 2 microfarads. Experiment has shown that this particular combination is effective over the range of frequencies to 70 kilocycles. It is not intended, however, to restrict the scope of this invention to that particular combination of capacity and inductance, as these values are determined by the range of frequencies within which the invention is required to function.

Furthermore, though the use of signal blockers for preventing wired radio signal reception has been emphasized herein, it is obvious that it may be advantageously employed on other types of wired radio circuits, for example street lighting systems, wherein high frequency currents superimposed upon the electric light and power wires are employed for relay control and operation. It is intended to extend the scope of this invention to cover such systems.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

l. In a system for transmitting programs by carrier frequency energy, power lines conveying both commercial power and program modulated carrier frequency energy at several different program carrier frequencies, said power lines having authorized and unauthorized program reception sections, low-pass filter means connected in said power lines forming an effective carrier frequency impedance lumped in the conductive path of said commercial power for preventing reception of said program energy at said unauthorized sections of said power lines for carrier frequencies substantially within the range of 25 to 75 kilocycles while permitting the passage of commercial power therethrough, said means comprising a conductive impedance system through which said commercial power is conducted substantially unaffected and designed to prevent the effective transmission therethrough of carrier energy to said unauthorized reception sections of said power lines at any and all of said several different program carrier frequencies whereby theft of programs by said unauthorized reception sections is prevented.

2. A wired radio system comprising conductors carrying commercial power and signalling energy at a plurality of program modulated carrier frequencies, authorized and unauthorized receiving apparatus, and low-pass filter means connected in circuit with said conductors for preventing the transmission of all of said carrier frequencies to said unauthorized receiving apparatus, said means comprising at least one series inductance adjacent said unauthorized receiving apparatus and in circuit therewith in said conductors carrying said commercial power and said signalling energy, said means also comprising at least one capacitative coupling across said power conductors on the side of said inductance adjacent said unauthorized receiving apparatus, said inductance and capacitance being designed to effectively block, without undue absorption, the signalling energy at all of said carrier frequencies whereby theft of the wired radio programs by unauthorized receiving apparatus is prevented.

3. In a system for broadcasting over metallic conductors, conductors conveying low frequency currents and program modulated carrier frequency currents simultaneously at different carrier frequencies, authorized and unauthorized receiving apparatus connected to said conductors and low-pass filter means connected in circuit with said conductors for preventing the transmission of said modulated carrier frequency currents at all of said frequencies, said means comprising at least one inductance adjacent and in series with said unauthorized receiving apparatus and at least one capacitative coupling across said conductors on the side of said inductance adjacent said unauthorized receiving apparatus, said inductance and capacitative coupling constituting an effective blocking device with respect to a frequency range of an extent encompassing all of said program modulated carrier frequencies while simultaneously affording a low impedance to said other currents impressed upon said conductors whereby theft of the wired radio programs by said unauthorized receivers is prevented.

4. In a system of broadcasting over metallic conductors, conductors carrying commercial alternating current and program modulated carrier frequency energy at a plurality of different carrier frequencies, authorized and unauthorized receiving apparatus, and low-pass filter means connected in circuit with said conductors for the prevention of transmission of all of said carrier frequencies to said unauthorized receiving apparatus, said means comprising at least one series inductance interposed in circuit between the source of said wired radio programs and said unauthorized receiving apparatus in combination with at least one capacitative coupling across the conductors which lead to said unauthorized receiving apparatus, said inductance and capacitative coupling constituting an effective barrier to the transmission therethrough of wired radio programs at said carrier frequencies to said unauthorized receiving apparatus while offering a low impedance to said commercial alternating current transmitted by said conductors and further offering an absorptive medium with respect to transient high frequency currents such as would interfere with the authorized reception of said wired radio programs whereby theft of the wired radio programs by said unauthorized receivers is prevented.

ROBERT D. DUNCAN, JR. 

